Bone anchoring device

ABSTRACT

A bone anchoring device includes an anchoring element having a shaft and a head, a receiving part having a coaxial bore and a seat for receiving the head, a pressure element configured to be movable within the bore, and a preload element being positionable between the head and the pressure element. When the head is inserted in the receiving part, the head is pivotable with respect to the receiving part, and can be locked at an angle relative to the receiving part by the pressure element. The pressure element can assume a position relative to the receiving part where the pressure element and the preload element are in direct contact, and where the pressure element exerts a force onto the head via the preload element to maintain one of a plurality of releasable angular positions between the head and the receiving part by friction before locking the head.

CROSS-REFERENCE TO RELATED APPLICATION(S)

The present application claims the benefit of U.S. Provisional Patent Application Ser. No. 61/426,776, filed Dec. 23, 2010, the contents of which are hereby incorporated by reference in their entirety, and claims priority to European Patent Application EP 10 196 880.8, filed Dec. 23, 2010, the contents of which are hereby incorporated by reference in their entirety.

BACKGROUND

1. Field of the Invention

The invention relates to a bone anchoring device for anchoring a stabilization rod to a bone or to a vertebra. The bone anchoring device includes a bone anchoring element and a receiving part for receiving a head of the bone anchoring element and for receiving a stabilization rod to be connected to the bone anchoring element. The bone anchoring element is pivotably connected to the receiving part and can be fixed at an angle by exerting pressure onto the head via a pressure element which may be arranged in the receiving part. The head has a recess which accommodates a closed ring which is configured to cooperate in such a way with the head and the pressure element that the pressure element can assume a position within the receiving part in which it clamps the head via the ring by friction without fully locking the head with respect to the receiving part.

2. Description of Related Art

US 2004/0267264 A1 describes a polyaxial fixation device, wherein the polyaxial bone screw includes an engagement member that is adapted to provide sufficient friction between the spherical head and the receiver member to enable the shank to be maintained in a desired angular orientation before locking the spherical head within the receiver member. The engagement member is realized, for example, by an open snap ring around the head or by spring members provided at the compression cap to frictionally engage the spherical head or by a slot provided in the compression cap.

SUMMARY

It is an object of the invention to provide a bone anchoring device which allows for improved handling during surgery and which can be manufactured cost-effectively in a simple manner.

With the bone anchoring device according to embodiments of the present invention, a temporary clamping of the head in a desired angular position with respect to the receiving part without locking the head can be achieved. This allows the receiving part to be held in an adjustable angular position. In this position the pressure element exerts a preload onto the head via the ring, such that the head is not locked but is frictionally prevented from freely pivoting. When the head is temporarily clamped, the alignment of the receiving part to the rod and the insertion of the rod is facilitated. In addition, when the rod is already inserted into the receiving part, adjustments of the rod are still possible without completely loosening the head within the receiving part. Finally, the pressure element can be pressed onto the head to lock the head in a desired portion.

In addition, the bone anchoring device has relatively few parts which are of simple design.

Furthermore, the heads of already manufactured bone anchoring devices can easily be upgraded to the system according to embodiments of the present invention. For example, in some embodiments, only a groove around the head and a closed ring which is accommodated by the groove have to be further provided.

The parts of the bone anchoring device can be manufactured in series at low costs.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features and advantages of the invention will become apparent from the description of embodiments by means of the accompanying drawings. In the drawings:

FIG. 1 shows a perspective exploded view of a bone anchoring device according to an embodiment of the present invention;

FIG. 2 shows the bone anchoring device of FIG. 1 in an assembled state;

FIG. 3 a shows a perspective view of a bone anchoring element according to an embodiment of the present invention;

FIG. 3 b shows a cross-sectional view of the bone anchoring element of FIG. 3 a, the cross-section being taken in a plane containing the screw axis;

FIG. 3 c shows a top view of the bone anchoring element of FIG. 3 a;

FIG. 4 a shows a perspective view of a ring according to an embodiment of the present invention;

FIG. 4 b shows a side view of the ring of FIG. 4 a;

FIG. 4 c shows a cross-sectional view of the ring of FIG. 4 a;

FIG. 4 d shows a top view of the ring of FIG. 4 a;

FIG. 5 a shows a cross-sectional view of the bone anchoring device of FIGS. 1 and 2 in an assembled state before final locking of a head of a bone anchoring element;

FIG. 5 b shows an enlarged portion of FIG. 5 a;

FIG. 6 a shows a cross-sectional exploded view of a bone anchoring element and a ring according to an embodiment of the present invention;

FIG. 6 b shows a cross sectional view of the bone anchoring element and the ring of FIG. 6 a in an assembled state;

FIG. 6 c shows an enlarged portion of FIG. 6 b; and

FIG. 6 d shows a cross sectional view of the bone anchoring element and the ring of FIG. 6 a and a pressure element in an assembled state according to an embodiment of the present invention.

DETAILED DESCRIPTION

A polyaxial bone anchoring device 1 according to a first embodiment, as shown in FIGS. 1, 2 and 5 a, includes a bone anchoring element 2 in the form of a screw member having a threaded shaft 3 and a head 4. The head 4 includes a tool recess 4 a at its free end for engagement with a tool (not shown) to insert the threaded shaft 3 into a bone. The bone anchoring device 1 further includes a receiving part 5 for connecting the screw member 2 to a rod 20. A pressure element 6 is arranged in the receiving part 5 on top of the head 4 (as illustrated). For securing the rod 20 in the receiving part 5 and for exerting pressure onto the head 4, a locking device, for example, an inner screw 7, which cooperates with the receiving part 5, is provided.

As shown in FIGS. 3 a, 3 b and 3 c, the head 4 is shaped as a spherical segment having a flat free end and having the tool recess 4 a at the flat free end. An annular groove 41 is provided at a position above a greatest diameter of the head 4 in a direction towards the free end. A cross-section of the annular groove 41 is substantially trapezoidal with an open side, as can also be seen in FIG. 6 a. The annular groove 41 is configured to accommodate a ring 8. A ground or innermost surface of the annular groove 41 is substantially coaxial with an axis of the screw member 2. The edges of the ground of the annular groove 41 can be rounded. In some embodiments, the free end of the head 4 can also differ from the described flat form.

The receiving part 5 is a substantially cylindrical one-piece part, and has a top end 51 and a bottom end 52. A passageway extending from the top end 51 to the bottom end 52 is formed by a coaxial bore 53 followed by a seat portion 54 for receiving the head 4 of the screw member 2. The seat portion 54 has an opening 55 at the bottom end 52 through which the shaft 3 of the screw member 2 can extend. The seat portion 54 is shown to be spherically-shaped, but can be tapered or can have any other shape that allows receiving of the head 4 so that the head 4 can pivot with respect to the receiving part 5. At the top end 51, a substantially U-shaped recess 56 is provided by means of which two free legs 57, 58 are formed that serve as sidewalls of a channel for receiving the rod 20. An internal thread 59 is provided on the legs 57, 58 for cooperating with the inner screw 7.

The receiving part 5 also has at a position closer to the bottom end 52 than to the top end 51 two blind holes 500 a, 500 b forming crimp bores that extend from an outer surface of the receiving part 5 to a distance from the inner wall of the coaxial bore 53, for crimping in a manner described below. The blind holes 500 a, 500 b may be arranged 180° offset from each other and at 90° with respect to the channel formed by the U-shaped recess 56. The blind holes 500 a, 500 b are aligned perpendicular with respect to a bore axis of the coaxial bore 53. The portions of the receiving part 5 that are between the closed ends of the blind holes 500 a, 500 b and the coaxial bore 53 of the receiving part 5 are configured to be deformable portions.

The pressure element 6 is formed in one piece. The pressure element 6 is of substantially cylindrical construction and has an outer diameter which allows it to move in an axial direction within the bore 53 of the receiving part 5. The pressure element 6 has a top end 61 and a bottom end 62. When the pressure element 6 is inserted into the receiving part 5, the bottom end 62 faces the head 4 of an inserted bone anchoring element 2. At the top end 61, a U-shaped recess 64 is provided by means of which two free legs 65, 66 are formed, forming a channel to receive the rod 20 therein. Furthermore, the pressure element 6 includes a coaxial bore 67 for providing access to the screw head 4 with a tool (not shown). As shown in FIGS. 1 and 2, the pressure element 6 is a solid member which is arranged in the receiving part 5, such that the U-shaped recess 56 of the receiving part 5 and the U-shaped recess 64 of the pressure element 6 can be aligned.

The pressure element 6 includes two crimp bores 600 a, 600 b corresponding to the crimp bores 500 a, 500 b of the receiving part 5, wherein after crimping, the pressure element 6 may be held in a rotationally aligned position and at an axial position in which the pressure element 6 can exert a slight preload onto the head 4.

FIGS. 4 a to 4 d show a ring 8 according to an embodiment of the present invention. As shown in FIG. 4 c the ring 8 is closed, and has a substantially circular cross-section in an undeformed state. The ring 8 may be made of a plastic material which is elastically deformable, for example a bio-compatible elastomer. As an elastomer, for example, UHMWPE (Ultra-high-molecular-weight polyethylene), Silicon, PCU, SIBS, or combinations thereof can be used. Other parts of the bone anchoring device 1 may be made of a body-compatible material, such as a body-compatible metal, for example, titanium, body-compatible metal alloys such as, for example, Nitinol, or from a body-compatible plastic material, such as, for example, PEEK, or combinations thereof.

The size of the ring 8 is such that when the ring 8 is inserted into the annular groove 41, the ring 8 is substantially undeformed and projects slightly out of the annular groove 41. Since the cross-section of the annular groove 41 is trapezoidal, the annular groove 41 provides space for the deformation of the ring 8 upon exertion of a load onto the ring 8 by the pressure element 6 (e.g., from above).

In an assembled state, as shown in FIG. 5 a, the head 4 is located in the seat 54 and the pressure element 6 is arranged on top of the head 4. The heights of the free legs 65, 66 of the pressure element 6 are configured such that the free legs 65, 66 do not extend above the rod 20 when the rod 20 is inserted and rests on the bottom of the channel of the pressure element 6. The pressure element 6, as shown in FIGS. 5 a and 5 b, can assume a first position which is defined by connecting the pressure element 6 and the receiving part 5 by crimping through the crimp bores 500 a, 500 b, and in some cases, 600 a, 600 b. In this manner, the ring 8 and the pressure element 6 cooperate in such a way that the pressure element 6 exerts a preload force onto the head 4 via the ring 8, where the head 4 may be maintained at an angular position by friction before finally locking the head 4. The three may be exerted onto the head 4 via the inner screw 7, the rod 20, the pressure element 6, and the ring 8. The ring 8, which has a substantially circular cross-section, may be deformed such that its cross-section is substantially oval in this first position. By the deformation, the ring 8 exerts a counter force onto the pressure element 6 so that the head 4 is maintained in an angular position. This position can be adjusted by applying a force to the bone anchoring element 2 or the receiving part 5 to overcome the friction force. The pressure element 6 can also assume a second position in which the head 4 is locked by further screwing in the inner screw 7. Furthermore, the pressure element 6 can assume third positions in which the head 4 is capable of freely pivoting. In the third position, the pressure element 6 is substantially not in frictional contact with the ring 8. By selecting the size of the ring 8 and the size of the annular groove 41, a desired friction force can be achieved.

FIGS. 6 a to 6 d show the assembly of the bone anchoring element 2 with the ring 8. The ring 8 is mounted on the head 4 of the bone anchoring element 2 and is accommodated by the annular groove 41, as shown in FIGS. 6 b and 6 c. FIG. 6 d shows the bone anchoring element 2 with a mounted pressure element 6. When moving the pressure element 6 downwards in a direction towards the shaft 3, the head 4 may be maintained at an angular position by friction.

In use, first, the bone anchoring device I may be provided in a pre-assembled state, with the pressure element 6 being in the first position in which the head 4 is temporarily frictionally clamped. Usually several bone anchoring devices 1 are utilized. The screw members 2 are then screwed into respective bones or vertebrae, and then the corresponding receiving parts 5 are pivoted by applying a force to overcome the clamping force, until each receiving part 5 has a desired orientation for insertion of the rod 20. Due to the temporary clamping, the receiving parts 5 are held in their respective angular positions. The rod 20, which connects the bone anchoring devices 1, is inserted and the inner screws 7 are tightened to move the pressure elements 6 downwards to lock the heads 4 so that the angular positions of the screw members 2 with respect to the receiving parts 5 are fixed. The rod 20 is then also fixed by the inner screws 7.

For the bone anchoring element, various different kinds of anchoring elements can be used and combined with the receiving part. These anchoring elements may include, for example, screws with different length, screws with different diameters, cannulated screws, screws with different thread forms, nails, etc. In some embodiments, the head and the shaft can also be separate parts which can be connected to each other.

Various kinds of receiving parts can also be used, in particular, receiving parts with different locking devices. For example, instead of using a one-part locking device such as the inner screw which locks the rod and the head simultaneously, two-part locking devices with an outer screw and an inner screw can be used. In this case the pressure element may have a U-shaped recess with legs extending above the rod. With the two-part locking device, the head and the rod can be fixed independently. Further, outer nuts, outer caps, bayonet locking devices, or various other kinds of locking devices can also be utilized. The shape of the receiving part is also not limited to the embodiment shown. For example, the receiving part can have an asymmetric end portion for allowing a greater pivot angle of the screw member to one side.

In a modified embodiment, the annular groove is not provided on the head, but rather on the inner wall of the receiving part or on the pressure element, for accommodating the ring. The ring and the head may cooperate in such a way that the pressure element exerts a preload force onto the head via the ring, where the head is maintained at an angular position by friction before finally locking the head 4.

In a further modification, a ring is provided which is made of a non-flexible material, such as PEEK, for example. Such a ring should only be slightly oversized with respect to the surface of the head, to ensure the frictional contact. Further, the ring's cross-section can also be substantially oval, rectangular, etc., or can also vary over the circumference of the ring.

It is also possible to use one or several flexible elements which are arranged in the annular groove of the head or the pressure element, instead of using one single ring. The cross-sections of these elements or the ring, respectively, may also vary.

In a further modification, the receiving part may be configured to allow the introduction of the bone anchoring element from the bottom end.

While the present invention has been described in connection with certain exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but is instead intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims, and equivalents thereof. 

1. A bone anchoring device comprising: an anchoring element having a shaft for anchoring in a bone and a head; a receiving part having a first end and a second end, a recess for receiving a rod, a coaxial bore extending from the first end in the direction of the second end, and a seat for receiving the head near the second end; a pressure element configured to be movable within the bore; and a preload element comprising a polymer material, the preload element being positionable between the head and the pressure element when the head, the pressure element, and the preload element are inserted into the receiving part; wherein when the head is inserted in the receiving part, the head is pivotable with respect to the receiving part, and can be locked at an angle relative to the receiving part by exerting pressure via the pressure element onto the head; and wherein the pressure element can assume a first position relative to the receiving part where the pressure element and the preload element are in direct contact, such that while the pressure element is in the first position, the pressure element exerts a force onto the head via the preload element to maintain one of a plurality of releasable angular positions between the head and the receiving part by friction before locking the head.
 2. The bone anchoring device of claim 1, wherein the pressure element can assume a locking position different from the first position, in which the pressure element presses onto the head such that the head is locked.
 3. The bone anchoring device of claim 1, wherein the preload element is positionable between the head and the pressure element in a radial direction when inserted in the receiving part.
 4. The bone anchoring device of claim 1, wherein the preload element s a closed ring.
 5. The bone anchoring device of claim 1, wherein the head has a groove sized to accommodate the preload element.
 6. The bone anchoring device of claim 5, wherein the head is spherical and has a free end, and wherein the groove is positioned closer to the free end in an axial direction than a portion of the head having a greatest diameter.
 7. The bone anchoring device of claim 5, wherein the head is spherical and has a free end, wherein a plane perpendicular to a longitudinal axis of the anchoring element includes a greatest diameter of the head, and wherein a larger portion of the groove is located on a side of the plane closer to the free end than on a side of the plane farther away from the free end.
 8. The bone anchoring device of claim 5, wherein when the pressure element is in the first position, the preload element projects out of the groove, such that there is a friction fit between the pressure element and the preload element.
 9. The bone anchoring device of claim 1, wherein the pressure element has a groove sized to accommodate the preload element.
 10. The bone anchoring device of claim 1, wherein the preload element comprises an elastomer material.
 11. The bone anchoring device of claim 1, wherein a cross-section of the preload element is substantially circular when the preload element is in an undeformed state.
 12. The bone anchoring device of claim 1, further comprising a fixation element for securing a rod in the recess.
 13. The bone anchoring device of claim 1, wherein a maximum diameter of the head in a direction perpendicular to a longitudinal axis of the anchoring element is larger than an opening at the second end of the receiving part.
 14. The bone anchoring device of claim 1, wherein when the pressure element is in the first position, the pressure element and the preload element are configured to be in direct contact at least when respective longitudinal axes of the anchoring element and the receiving part are parallel.
 15. A method of coupling a rod to a bone via a polyaxial bone anchoring device, the bone anchoring device comprising: an anchoring element having a shaft for anchoring in a bone and a head; a receiving part having a first end and a second end, a recess for receiving a rod, a coaxial bore extending from the first end in the direction of the second end, and a seat for receiving the head near the second end, a pressure element configured to be movable within the bore, and a preload element comprising a polymer material, the method comprising: inserting the bone anchoring device into a bone when the pressure element is in a first position relative to the receiving part, and the preload element is in direct contact with the pressure element and positioned in the receiving part between the head of the anchoring element and the pressure element, such that while the pressure element is in the first position, the pressure element exerts a force onto the head via the preload element to maintain one of a plurality of releasable angular positions between the anchoring element and the receiving part by friction; applying a force onto the receiving part that is greater than a force of the friction to adjust the angular position between the anchoring element and the receiving part; inserting a rod into the channel; and advancing a fixation element into the channel to push the rod against the pressure element and the pressure element against the head to lock the angular position between the anchoring element and the receiving part via pressure from the pressure element on the head.
 16. The method of claim 15, wherein prior to inserting the bone anchoring device into the bone, the method further comprises: inserting the head of the anchoring element and the preload element into the receiving part; and inserting the pressure element into the receiving part.
 17. The method of claim 16, wherein prior to inserting the head of the anchoring element and the preload element into the receiving part, the method further comprises inserting the preload element into a groove provided on the head.
 18. The method of claim 16, wherein after inserting the pressure element into the receiving part, the method further comprises adjusting at least one of the receiving part or the pressure element to hold the pressure element in the first position and to prevent the pressure element from falling out of the receiving part. 